In this project we determined the antigenic relationships based on VP4 and VP7 neutralization specificities of various rotavirus strains derived from humans and animals. The elucidation of the neutralization specificities of rotaviruses is important in order to achieve a more comprehensive understanding of rotavirus epidemiology and for formulation of an effective strategy for vaccination. By using various single gene substitution human x human or human x animal rotavirus reassortants and hyperimmune guinea pig antiserum raised against each reassortant, we determined that (i) human rotavirus strain Se585 which was isolated in Seattle, WA, during strain surveillance conducted by CDC, belonged to an uncommon G12 serotype that had been isolated thus far only in the Philippines, (ii) strains CC425 and KC814 carried P3[9] specificity, which was the first detection in the US of a P[9] virus, and (iii) a small outbreak of diarrhea (n=16) in Rio de Janeiro, Brazil, in 1998-1999 was caused by a rare G3,P3[9] virus (Santos). In addition, we characterized VP4 neutralization specificities of a porcine rotavirus Gottfried strain (P1B[6],G4) and showed there was a one-way relationship between Gottfreid VP4 and human rotavirus VP4 with P[6] specificity, in which the human rotavirus was the prime strain. In addition, in collaboration with Food and Drug Administration (Chizhikov), we have established an oligonucleotide microarray assay to G genotype human rotaviruses.